Polybius Square

  • The Polybius square was a system for simplifying Telegraphy and Cryptography, devised by the Greek Historian Polybius (c. 200-118 BCE).
  • Once a message was coded it could be transmitted using Roman Signalling.

Transmitting Letters

  • The 24 letters of the Greek Alphabet were arranged in a 5 x 5 square. (The Roman Alphabet also only had 24 letters: J, U and W were missing).

 

1 (I) 2 (II) 3 (III) 4 (IV) 5 (V)
1 (I) A B C D E
2 (II) F G H E I
3 (III) K L M N O
4 (IV) P Q R S T
5 (V) V X Y Z
  • Words were then converted into numbers, for example:
    • ‘NERO’ becomes numbers 34 – 15 – 43 – 35
    • Or in visible Roman Numerals using Flags: III IV – I V – IV III – III V

Fire Signalling

  • It was much easier to transmit at night using Flaming Brands instead of Flags.
    • By Day:   Two groups of 5 flags on poles behind a screen.
    • By night: Two groups of 5 firebrands on poles behind a screen.

Transmitting Numbers

  • To transmit numbers the square is expanded into 6 x 6, and the numbers might have been added thus:
  • _1_2_3_4_5. .6
  • 1. A B C D E….VI
  • 2. F G H E I….VII
  • 3. K L M N O…VIII
  • 4. P Q R S T…..IX
  • 5. V X Y Z ……..X
  • 6. I II III IV V…XI
  • ‘Number 9’ becomes: 46 (shows IX)(In visible flags: IV VI)
  • ;Number 109′ becomes: 13 (C is 100) 46 (shows IX)

 

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